Perl has a useful magic filehandle called *ARGV that checks the command line and if there are any arguments, opens and reads those as files. If there are no arguments, *ARGV behaves like *STDIN instead. This behavior is almost always what you want if you want to create a program that reads from STDIN. This is often written in one of the following two equivalent forms:

  while (<ARGV>) {
    # ... do something with each input line ...
  # or, equivalently:
  while (<>) {
    # ... do something with each input line ...

If you want to prompt for user input, try special purpose modules like the IO::Prompt manpage.


Due to a bug in the current version of PPI (v1.119_03) and earlier, the readline operator is often misinterpreted as less-than and greater-than operators after a comma. Therefore, this policy misses important cases like

  my $content = join '', <STDIN>;

because it interprets that line as the nonsensical statement:

  my $content = join '', < STDIN >;

When that PPI bug is fixed, this policy should start catching those violations automatically.


Initial development of this policy was supported by a grant from the Perl Foundation.


Chris Dolan <cdolan@cpan.org>


Copyright (c) 2007 Chris Dolan. Many rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of this license can be found in the LICENSE file included with this module